This disclosure generally relates to articles coated with protective materials. More particularly, this disclosure relates to articles coated with oxidation- and corrosion-resistant coatings for use at high temperature, and methods for fabricating such articles.
Materials used for high-temperature applications, such as, for instance, gas turbine assembly components, are typically optimized to provide excellent mechanical properties at high temperatures. This optimization often sacrifices somewhat the resistance of the materials to high temperature corrosion and oxidation. To improve the overall performance of components made with such materials, coatings of various types are often applied to enhance component surface properties. For example, a substrate made of a nickel-based superalloy may be coated with an oxidation-resistant material such as a so-called “MCrAlX” coating, that is, a coating that includes chromium, aluminum, and (as represented by the generic “M”) one or more of nickel, cobalt, and iron. The optional “X” component of the coating, if present, is typically one or more additional elements, such as yttrium, rare earth elements, or reactive elements added to enhance certain properties of the material.
MCrAlX and other coatings are typically applied using thermal spray techniques. For example, combustion thermal spray devices are currently used to produce metallic coatings through particle melting, or partial melting, and acceleration onto a substrate. Such devices use a combustion process to produce gas temperatures above the melting point of the particles and gas pressures to impart velocity to the particles. One common problem encountered in the combustion thermal spray process is the susceptibility of the sprayed metal powder to oxidation. It is important to reduce the amount of oxygen present in the metal coating to improve the formability of the coating, and to make the coating less brittle.
Combustion cold spray techniques such as those disclosed in commonly assigned U.S. patent application Ser. No. 12/790,170 have been developed to enable formation of dense deposits of materials without substantially heating the materials above their melting points. While these techniques have provided attractive results, under certain conditions articles coated using these techniques have shown sub-optimal mechanical performance. Thus, there remains a need for coated articles that minimize performance debits attributable to the presence of the coating, and for methods for producing such articles.